The present invention relates generally to a process and apparatus for mixing and aerating a fluid stream by circulating a first fluid through a pulse spilled self-aerator (PSSA) such that a vacuum is generated at one or more discrete points thereby entraining a second fluid into the circulating fluid. More specifically, this process provides a method and apparatus for energy efficient self-aeration in chemical, biochemical, and wastewater treatment processes.
Large quantities of low-pressure air are required in aeration systems to support many biochemical production processes and wastewater treatment plants. Oxygen is traditionally supplied and mixed by a compressor or blower and a mechanical agitator. These systems have high-energy requirements and high installation and maintenance costs. Aeration, agitation, and oxygen transfer to aqueous phase are important in aerobic fermentation processes. Various fermentation systems are designed to meet the oxygen requirement of aerobic microorganism cultures for the production of amino acids, enzymes, and cell biomass, among others. One of the most commonly used systems is the aerated stirred tank reactor, which requires both an air compression system and an agitation system to provide oxygen to the culture as well as mixing. In this system, the reactor is equipped with a motor mounted on top of the reactor, which drives a shaft through the top of the reactor vessel down to the bottom of the reactor. Consequently, the shaft drives flat-blade turbines attached to the shaft for fluid mixing and bubble breaking for oxygen transfer into reaction broth. An aseptic seal is placed between the shaft and reactor vessel for sterile control. An air compression system is used to provide sterile air through a series of air processing equipment, typically containing air storage tank, oil removing tank, water removing rank, air heater, and air filter. The sterile air is aerated into the reactor through an air sparger on the bottom of the reactor. In general, the aerated stirred tank reactor system is of high performance, however, rather complicated and with high power input.
To maintain the reactor performance and simplify the reactor system as well as to lower the energy efficiency for gas dispersion and mixing, reactors with self-aspirating capability were also developed. These types of reactors include self-aspirating reactor with a rotor and a surrounding stator, and similar reactor serial with a special design rotor for aeration and mixing. This type of reactor eliminates the air compression system by a self-aspirating rotor and a distribution stator. The rotor is generally placed on the bottom of the reactor and submerged in the reaction broth. The rotor rotates at high speed and generates a vacuum in the rotor center, connected to the hollow shaft to induce air into the reactor system. The rotor performs both aeration and fluid mixing at the same time. This type of reactor system is rather energy efficient and simple in structure. However, the rotor self-aspirating reactor still has large fast moving parts inside the reactor and the maintenance is significant through a manhole on top of the reactor. Another type of self-aerating reactors, Venturi-type reactor serials were also developed using a special design nozzle for aeration and mixing. This type of reactor applies the Venturi tube principle that a vacuum can be created behind an orifice, through which high pressure or high velocity fluid passes. An air inlet can be opened after the orifice or nozzle for air induction. Air can be automatically sucked into the Venturi device and mixed with the oncoming fluid for air bubble dispersion and oxygen transfer. The high velocity air-fluid mixture is ejected into the reactor to mix with the main body of the reaction broth for further oxygen and nutrient transfer. The Venturi type of reactor further simplifies the agitated aerobic reactor system by removing the rotor or turbine impeller inside the reactor. However, this type of reactor requires high fluid pressure at the nozzle, which is in general driven by a high-speed circulation pump.
Therefore, it is apparent that there is a need in the industry for a mixing and/or aerating device that has few or no moving parts, low maintenance requirements, high efficiency, efficient mass transfer, low operational costs, and requires low capitol investment.
A method and apparatus is disclosed for mixing and agitating a fluid stream by circulating a first fluid through a pulse spilled self-aerator (PSSA) such that a vacuum is generated at one or more discrete points within the PSSA, providing a fluid mixture by entraining a second fluid into the circulating first fluid at the location of one or more discrete points via said vacuum, mixing and agitating the fluid mixture by a pulsing flow aided by gravitation flow vertically down one or more concentric units having at least one straight duct and at least one fluid pulsing unit. While the invention is preferably disclosed in the environment of aeration of liquid streams, it is to be understood that the process and apparatus of the present invention is applicable to the mixing of any fluid-like streams, whether liquid, solid or gaseous.
It is therefore an object of this invention to provide a method and apparatus for mixing and aerating a fluid stream in chemical, biochemical and wastewater treatment processes.
It is a further object of this invention to provide a system for mixing and aerating a fluid stream that is simple in construction.
It is another object of this invention to provide a system for mixing and aerating a fluid that requires low power consumption.
It is yet another object of this invention to provide a system for mixing and aerating a fluid that requires low capital investment.
It is another object of this invention to provide a system for mixing and aerating a fluid with efficient mass transfer.
It is yet another object of this invention to provide a system for mixing and aerating a fluid with low maintenance requirements.
It is another object of this invention to provide a system for mixing and aerating a fluid with low operational costs.
It is yet another object of this invention to provide a system for mixing and aerating a fluid with low operational noise.
It is another object of this invention to provide a system for mixing and aerating a fluid that allows for further enhancement of aeration by offering multiple PSSA""s to be used in a fluid system.